A gas turbine engine, typically used as a source of propulsion in aircraft or for power generation, largely operates by drawing in ambient air into a compressor, mixing that compressed air with a fuel in a combustor, igniting the air and fuel mixture, and then directing the resulting exhaust gases from the combustion process into a turbine.
Typically, an igniter generates an electrical spark to ignite the air-fuel mixture. The products of the combustion and the remains of the air-fuel mixture then travel out of the combustion chamber as exhaust and through the turbine. The turbine, having a plurality of blades extending from a center body, is forced to rotate as the exhaust passes through the turbine blades. The turbine and the compressor are connected to a common shaft running through the center of the engine. Thus, as the turbine rotates due to the influx of the expanding exhaust gases, the compressor in turn is caused to rotate and bring in and compress new air. Once started, it can thereby be seen that this process is self-sustaining.
Combustion chambers for gas turbine engines typically are annular in shape, and are defined by a combustor shell having a liner. An air passage is typically formed between the combustor shell and the liner to provide cooling air. More specifically, the combustor shell may include an outer combustor shell and an inner combustor shell, each having an associated liner. An outer liner may be disposed radially inside the outer shell and an inner liner may be disposed radially outside of the inner shell. The combustion chamber is the resulting annular space defined between the inner and outer liners.
In such a combustor, one or more igniters are disposed circumferentially around the annular combustion chamber, with each igniter typically being disposed in an opening extending through the outer combustor shell and the outer liner and into the combustion chamber. A separate opening is provided for each igniter. In some combustion chambers, the liners may be segmented into panels, with one of the panels of the outer liner being designated as an igniter panel and having the aforementioned openings for disposition of the igniters.
The air exiting the compressor in such an engine is typically split or bifurcated, with a portion of the compressed air being used for combustion, and a portion of the compressed air being used for cooling purposes. To prevent the compressed air typically used for cooling the combustion chamber from entering the combustion chamber through the openings provided for the igniters, a seal and grommet are typically disposed around each igniter. But for such seals, any influx of the cooling air around the igniters may degrade engine performance in terms of reliable ignition, maintenance of the proper ratio of air to fuel, and disruption of the flow of the air-fuel mixture in the combustion chamber.
While effective, as gas turbine combustion engines have advanced, temperatures in the combustion chamber, and more specifically the areas around the igniters, have increased during operation. These increased temperatures can detrimentally affect engine components, including the outer liner and outer combustor shell. For example, a crack in the outer liner and/or outer combustor shell in the area around the igniter can form from excessive heating of the area around the igniter. Deformations of the outer liner and/or outer combustor shell can also cause degradation in igniter performance, thereby decreasing engine efficiency and possibly necessitating repair or replacement of such components.